Certain polyesters are known in the art to be useful in adhesive applications; however, these adhesives suffer several disadvantages (see, for example, U.S. Pat. No. 4,618,643).
Polyester adhesives are normally used in powder, film, or web form for bonding and laminating applications. They can be processed easily in extruders where temperatures can be raised to obtain the lower melt viscosities needed for the application. With certain hot-melt adhesive application systems such as hand-held glue guns, it is not practical or safe to use processing temperatures greater than 190.degree. C. or adhesives with melt viscosity values greater than about 50,000 centipoise (cP) at 190.degree. C. for preparing bonds. Most polyester adhesives have melt viscosity values in the range of about 75,000 to about 300,000 cP at 190.degree. C. and are not suitable for these applications. In general, if the inherent viscosity (I.V.) of polyesters is reduced to levels so that the melt viscosity at application temperature is less than about 50,000 cP, the bonding properties of the polyester adhesive for hot-melt applications are often reduced to an unacceptable level due to faster crystallization times and shorter open time of the adhesive and the reduced tensile strength of the bulk polymer.
It would be desirable to have a polyester or formulation thereof that has excellent bonding properties and acceptable melt viscosity for glue gun adhesive applications.